As a secondary battery is a battery which converts chemical energy into electrical energy to supply power to an external circuit and, when the battery is discharged, receives external power and converts electrical energy into chemical energy so that electricity is stored therein, the secondary battery is generally referred to as a storage battery.
Such secondary batteries include lead storage batteries, nickel-cadmium secondary batteries, lithium secondary batteries, and so on. A lead storage battery is used for a vehicle because the lead storage battery has a high voltage but is bulky and heavy, a nickel-cadmium secondary battery is used as a substitute for a dry cell, and a lithium secondary battery is used for a power source of cameras, mobile phones, and so on because the lithium secondary battery is very light. The lithium secondary batteries among the above described secondary batteries have been widely used due to popularization of personal portable terminals such as smart phones and tablet personal computers (tablet PCs), which have been rapidly increasing recently.
However, in a lithium secondary battery, lithium as a main material is considerably expensive, and when a lithium secondary battery of which lifetime is over is discarded, there is a problem in that lithium is discharged from a waste disposal place and environmental pollution is involved.
Therefore, there is an urgent need to develop a high-power secondary battery that can replace a lithium secondary battery.